It has been proved that when the chromium ratio is high, the thermal stability of refired magnesite decreases with the increase or decrease of chromium and magnesium. When the content of chromium ore is too high, the resistance of the product to the action of iron oxide at 1650℃ will be significantly reduced. Chromium ore particles can form a solid solution with Fe2O3, causing a sharp expansion of the volume, resulting in the product burst phenomenon. The higher the content of chromium ore in the ingredients, the more serious the explosion. The increase of magnesia content in the ingredients can enhance the slag resistance of the product.
Dead burned magnesite article composed of magnesium spinel ashlar. The matrix part is composed of silicate. The main minerals in the silicate matrix are M2S, CMS, C3MS2, etc. Except for M2S, CMS and C3MS2 are both low-melting minerals. Therefore, the CaO content in the raw materials should be limited and the matrix minerals in the bricks should generate high refractory M2S.
When dead burned magnesia is fired into high-quality fire materials under the atmosphere, at 650℃, the solid phase reaction of MgO in the fine magnesia powder replacing the FeO of the spinel in the coarse-grained chrome ore begins to occur. Such a large volume shrinkage is bound to occur. Fire cracks are produced. And FeO replaced by MgO in an oxidizing atmosphere is oxidized to Fe2O3, and then combined with MgO magnesium ferrite. Accordingly, chromium-magnesia refractories should be fired in a weakly oxidizing atmosphere.